JP3017167B2 - Method and apparatus for binarizing a read signal from a data storage medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a method for reducing a bit error rate generated when data is reproduced from a medium in which the data is stored. With regard to
More particularly, it relates to a method and apparatus for more accurately binarizing a read signal from a medium in which data is stored.

[0002]

2. Description of the Related Art Magnetic disks (HD), digital video disks (DVD), magneto-optical disks (MO), and the like are used as storage media for information (data) such as documents, images, and sounds.
Compact disc (CD), laser disc (L
D) and other storage media have been developed, and their capacities are currently increasing.

When reproducing data from a medium storing data such as an optical disk, a read signal from the medium is binarized as bit string (digital) information consisting of "1" and "0". There is a need to. FIG. 1 is a diagram showing a method (principle) for binarizing a read signal from a medium recorded by a PWM method. In FIG. 1, reference numeral 1 denotes a read signal from a medium, and reference numeral 2 denotes a slice level signal for binarization (hereinafter, referred to as a "slice signal"). The slice signal is usually determined by a digital sum value circuit (DSV) having an integrating circuit as an average of the integrated value of the output signal from the medium. Reference numeral 3 represents a clock for binarization, and is hereinafter referred to as a "time cell" in this specification. The time cell 3 is usually determined and controlled by a phase lock loop (PLL) based on the frequency of the output signal from the medium. The time cell 3 has a fixed phase “1π to +
π ".

In FIG. 1, a time cell including an intersection 6 of a read signal 1 and a slice signal 2 has a bit "1". A time cell that does not include an intersection has bit “0”. As a result, as shown by reference numeral 7 in FIG. 1, the read signal 1 is converted into bit string information composed of "1" and "0".

[0005] The reproduced bit string information changes due to a change in the slice level of the slice signal 2 and a change in the width (period) of the time cell. For example, as shown in FIG. 2, when the slice level of the slice signal shifts upward from the original position 8 and shifts to the position 9 indicated by the dotted line, the position of the intersection with the lead signal 1 matches. 10,
It shifts back and forth as indicated by 11. as a result,
The time cell that should contain the intersection deviates from the cell that should be.

Further, an error is included at the intersection of the read signal and the slice signal due to the influence of signal waveform distortion caused by noise. FIG. 3 shows the slice level variation and the measured phase error within one time cell.
FIG. 9 is a diagram showing the influence of (fluctuation). In FIG.
Reference numeral 2 denotes a phase value shift due to a change in slice level. The three measured values A, B, and C at the intersection each have an error width 13 of the measured values. In FIG. 3, the polarity is corrected for each phase error, and the error is displayed using only positive values. The measured value C may exceed the phase “+ π” due to an error and exist in an adjacent time cell. That is, there is a high possibility that the time cell that should include the intersection is shifted. The shift of the time cell including the intersection also occurs when the width (period) of the time cell increases or decreases. As a result, there is a high possibility that the reproduced bit string information is different from the true data that should exist.

[0007] The reproduced bit string information is then inspected by an error correction circuit (ECC) to correct the error. However, the correction is not always complete. Therefore, it is effective if a correction corresponding to the error correction of the bit string information reproduced by some other method can be performed.

[0008] Further, bit string information obtained by reproducing an "ID" or the like in a preformat portion of an optical disk or the like cannot be corrected by ECC. Therefore, it is very effective if these data which cannot be corrected by the ECC can be corrected by any method and reproduced more accurately. This is because "SM", "VFO", and the like are usually located before an area (sector) in which storage data exists, and if accurate reproduction cannot be performed, storage data cannot be reproduced or written in sector units. It is because.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for more accurately binarizing a read signal from a medium in which data is stored.

A further object of the present invention is to select a likely time cell containing an intersection by evaluating the phase error at the intersection of a read signal and a slice signal from a medium in which data is stored. And a method and apparatus for reproducing correct bit string information.

It is a further object of the present invention to provide a method and an apparatus which can reduce the occurrence of bit error rate in reproducing stored data.

[0012]

According to the present invention, there is provided a method for binarizing a read signal from a medium in which data is stored, comprising the steps of: Determining a cell cycle; detecting an intersection between the read signal and the slice signal; selecting a time cell including the intersection; and setting the reselected time cell to bit "1". and determining seen including, before
Assess the certainty of the time cell and include intersections
The step of reselecting the time cell to
In each of the imcell and the two time cells before and after it
Determining the phase difference between the mind and the intersection;
Identify the time cell selected using the three phase differences
The intersection is included from among the three time cells.
Determined to be the most likely time cell
Selecting a time cell to be used.
How to and are provided.

According to the present invention, there is provided an apparatus for binarizing a read signal from a medium in which data is stored, comprising: a circuit for generating a slice signal; A level comparator for slicing the read signal and detecting an intersection of the read signal and the slice signal, a circuit for generating and controlling the time cell, and an intersection using the detected phase difference. An operation evaluation circuit for evaluating the likelihood of the included time cell and selecting a time cell in which the intersection should be included , wherein the operation evaluation circuit
Time cell and the two time cells before and after it
Find the phase difference between each center and the intersection, and find the three
Of the time cell selected using the phase difference of
Evaluate, and then, from among the three time cells,
Is most probable as a time cell that should be included
Selecting a time cell to be performed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 is a diagram for explaining an embodiment of the present invention, showing a relationship between an intersection of a read signal and a slice signal from a storage medium and a time cell. In addition,
Storage media include magnetic disks (HD), digital
Video disk (DVD), magneto-optical disk (M
O), compact discs (CD), laser discs (LD) and any other storage media. FIG.
5 shows an example in which the lead signal 15 is distorted due to the influence of noise or the like with respect to the lead signal waveform 16 which should be originally detected. Since the waveform of the read signal 15 is distorted, the intersection 18 with the slice signal 17 is shifted to the left from the position where it should be (to advance in time).
Has been done. Reference numerals 19, 20, and 21 indicate time cells. The width of the time cell (period)
Is determined based on the frequency of the read signal.

The phase difference between the center of the time cell 19 including the intersection 18 and the intersection 18 is “θ”, and the phase difference between the center of the left and right time cells 20 and 21 of the time cell 19 and the intersection 18 is “θ−”. 1 "and" θ + 1 ". In FIG. 4, the intersection 18
Is to the right of the center of the time cell 19,
The signs of “θ” and “θ−1” are positive, the sign of the phase difference “θ + 1” is negative, and the absolute value of the phase difference is “θ + 1”
θ-1 ". Here, the smaller phase difference of this absolute value is denoted by φ. In the example of FIG. 4, the smaller phase difference is"
If the sign of the phase difference “θ” is negative and the absolute value of the phase difference “θ-1” is smaller than “θ + 1”, The phase difference “θ-1” is set as φ.

From the phase differences θ and φ, the value two before (phase difference) p (0) and the value immediately before (phase difference) p (1), the following two Two straight lines L0 and L1 are obtained. L0 = f (p (0), p (1), θ) L1 = f (p (0), p (1), φ) FIG. 5 shows an example of FIG. FIG. 7 is a diagram showing the obtained straight lines L0 and L1. The straight line L0 is a straight line (solid line) obtained from the three points p (0), p (1), and θ by the least squares method.
This is a straight line (dotted line) obtained from the three points p (0), p (1), and φ by the least square method.

Next, using the obtained straight lines L0 and L1, the distance D0 between the straight line L0 and the point p (1) and the straight line L1
The distance D1 of the point p (1) is obtained. Then, the smaller one of the distances D0 and D1 is selected as a likely phase difference. Here, instead of the distances D0 and D1, a straight line L
Sum D of the distance between 0 and 3 points p (0), p (1) and θ
0, and the sum D1 of the distance between the straight line L1 and the three points p (0), p (1), and φ, and similarly, the smaller one of D0 and D1 may be selected as a likely phase difference. .

A time cell containing the selected phase difference is selected as a likely time cell that should contain an intersection. That is, if D0 <D1, the time cell 19 having θ is selected as a likely time cell. vice versa,
If D0> D1, the time cell 21 having φ (“θ + 1” in the example of FIG. 4) is selected as a likely time cell. If D0 = D1, a time cell including θ is selected. Thereby, even if the phase difference exceeds π, it is possible to select a probable time cell. However, in the example of FIG. 4, errors that can be selected (corrected) are limited to the range of one time cell before and after the time cell having “θ”. Finally, the previous value (phase difference) p
(1) is newly stored as p (0), and the selected θ or φ is newly stored as p (1) to prepare for the next evaluation. Then, each time a new intersection measurement value is obtained, a similar selection determination is performed.

FIG. 6 is a flowchart of the embodiment described above.
Shown in Although this embodiment is an example in which the error is evaluated using the least squares method, the evaluation can be performed by a method other than this method.

For example, first, the average value α of the past selection values p (0), p (1),..., P (i-11) before the current measurement value p (i) is obtained. Next, the average value α and the phase difference “θ”
(FIG. 4), the average value α and the phase difference “θ−
The distance d2 from the smaller phase difference φ of 1 "and" θ + 1 "(FIG. 4) is obtained, and the smaller one of the distances d1 and d2 is selected as a likely phase difference. Is selected as a likely time cell that should contain an intersection, ie, d1 <d.
If 2, the time cell 19 having θ (FIG. 4) is selected as a likely time cell. Conversely, if d1> d2, the time cell 21 having φ (“θ + 1” in the example of FIG. 4)
(FIG. 4) is selected as a likely time cell. If d1 = d2, the time cell 19 containing θ
Select

As another example, first, a linear function F is obtained from past selection values, p (0), p (1), and p (2). Next, a linear function F is extrapolated to predict the current observation value β. FIG. 6 is a diagram showing this state. In FIG. 6, a distance d3 between the observed value β and the phase difference “θ” and a distance d4 between the observed value β and the phase difference φ are obtained. And the distance d3
And the smaller one of d4 is selected as a likely phase difference. The time cell containing the selected phase difference is selected as a likely time cell that should contain the intersection.
That is, if d3 <d4, time cell 1 having θ
9 (FIG. 4) is selected as a likely time cell. Conversely, if d3> d4, the time cell 21 (FIG. 4) having φ (“θ + 1” in the example of FIG. 4) is selected as a likely time cell. If d3 = d4, a time cell including θ is selected.

FIG. 8 is a diagram showing an embodiment of an apparatus for binarizing a read signal from a data storage medium according to the present invention. The binarization device 30 includes a DSV operation circuit 32, a level comparator 33, a circuit (digital PLL) 35 for generating and controlling a time cell, a phase comparator 34, and an operation evaluation circuit 36. .

In the apparatus shown in FIG.
Generates a slice signal. The level comparator 33 receives the read signal 31 from the data storage medium and the slice signal from the DSV operation circuit 32, and detects an intersection between the read signal and the slice signal. The phase comparator 34 selects a time cell including the detected intersection, and detects a phase difference between the center of the time cell and the intersection. Time cell is PLL
Feedback control is performed by 35. The operation evaluation circuit 36 evaluates the likelihood of the time cell including the intersection using the detected phase difference, and selects a time cell that should include the intersection. More specific evaluation in the arithmetic evaluation circuit 36 is performed using a binarization method using the above-described least square method or the like.

As described above, according to the present invention, when the read signal from the data storage medium is more accurately binarized, the read signal from the data storage medium is sliced with the slice signal. By evaluating the phase error at the intersection of the signals, it is possible to select the likely time cell containing the intersection, reproduce the correct bit string information, and reduce the occurrence of bit error rate during reproduction. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method (principle) for binarizing a read signal from a storage medium.

FIG. 2 is a diagram showing a state of a change in a slice level of a slice signal.

FIG. 3 is a diagram showing the influence of a slice level fluctuation and a measurement value phase error (fluctuation) within one time cell.

FIG. 4 is a diagram showing a relationship between an intersection of a read signal and a slice signal from a storage medium and a time cell.

FIG. 5 is a diagram showing straight lines L0 and L1 obtained by the method of the present invention and obtained by using the least squares method.

FIG. 6 is a diagram showing a flow of the method of the present invention.

FIG. 7 is a diagram showing a straight line F obtained by the method of the present invention.

FIG. 8 is a diagram showing an embodiment of the binarization device of the present invention.

[Explanation of symbols]

 1, 15, 16, 31 Read signal 2, 17 Slice signal 3, 19, 20, 21 Time cell 4 Phase 6, 18 Intersection 7 Bit string information 8, 9 Slice level 10, 11 Intersection shift 12 Slice level 13 Deviation of measured value 30 Binarization device 32 DSV operation circuit 33 Level comparator 34 Phase comparator 35 PLL 36 Operation processing circuit

────────────────────────────────────────────────── (5) References JP-A-5-167569 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 20/10 321 G11B 20/14 341

Claims (13)

(57) [Claims] 1. A method for binarizing a read signal from a medium in which data is stored, comprising the steps of: determining a period of a time cell from a frequency of the read signal; Detecting the intersection of the intersection signal and the slice signal, selecting the time cell including the intersection, evaluating the likelihood of the selected time cell, and reselecting the time cell that should include the intersection. When, viewed it contains and determining the bit "1" to time cells re-selected, to evaluate the likelihood of the time cell, include intersection
The step of re-selecting the time cell to be executed is composed of the selected time cell and two time cells before and after the selected time cell.
The phase difference between each intersection of the center and the intersection
And a time cell selected using the obtained three phase differences
Is evaluated, and from among the three time cells,
Most likely time cell that should contain an intersection
Method characterized by comprising the steps of: selecting a time cell that is determined to be. 2. Assessing the likelihood of the time cell,
The step of selecting the most probable time cell comprises the following two straight lines L0 and L1 using the least squares method.
L0 = f (p (0), p (1), θ) L1 = f (p (0), p (1), φ) where θ: the center of the time cell at which the intersection is detected The phase difference between the intersection and the intersection, φ: the phase difference θ-1 or θ + 1 between the center of each of the two time cells before and after the time cell at which the intersection is detected and the intersection and the smaller absolute value Phase difference, p (0): value two times before (phase difference), p (1): previous value (phase difference), distance D0 between straight line L0 and p (1), and distance D1 between straight line L1 and p (1) And selecting the smaller of D0 and D1 as a probable sum, and using the selected D0 or D1 as a probable time cell containing θ or φ as the probable time cell at which the intersection should be included. the method of claim 1 further comprising a step of selecting, the. 3. Assessing the likelihood of the time cell,
The step of selecting the most probable time cell comprises the following two straight lines L0 and L1 using the least squares method.
L0 = f (p (0), p (1), θ) L1 = f (p (0), p (1), φ) where θ: the center of the time cell at which the intersection is detected The phase difference between the intersection and the intersection, φ: the phase difference θ-1 or θ + 1 between the center of each of the two time cells before and after the time cell at which the intersection is detected and the intersection and the smaller absolute value Phase difference, p (0): value two times before (phase difference), p (1): previous value (phase difference), sum A0 of distances between straight line L0 and p (0), p (1), and θ Determining the sum A1 of the distances between the straight line L1 and p (0), p (1), and φ; selecting the smaller one of A0 and A1 as a likely sum; and selecting the selected A0 Or a time cell containing θ or φ based on A1 as a likely time cell that should contain the intersection The method of claim 1 further comprising a step of selecting, the. 4. Assessing the likelihood of the time cell,
The step of selecting the time cell determined to be most probable is a step of obtaining an average value α of the phase difference selected up to the previous time, and a step between the average value α and the center of the currently selected time cell and the intersection. And the average value α of the phase difference θ with respect to the phase difference θ,
Obtaining a distance d2 between the center of each of the two time cells before and after the currently selected time cell and the smaller of the phase difference φ of the phase difference θ-1 and θ + 1 between the intersection; Selecting a smaller one of d1 and d2 as a likely distance; selecting a time cell including θ or φ as a time cell that should include the intersection based on the selected d1 or d2; the method of claim 1 further comprising. 5. Evaluating the likelihood of the time cell,
Selecting a time cell determined to be most probable includes: obtaining a linear function F from the phase difference selected up to the previous time; extrapolating the linear function F to predict a current observation value β; An observed value β, a distance S1 between the center of the currently selected time cell and the phase difference θ between the intersection, and an observed value β;
Obtaining a distance S2 between a smaller phase difference φ of the phase differences θ-1 and θ + 1 between the center of each of the two time cells before and after the currently selected time cell and the intersection; Selecting a smaller one of S1 and S2 as a likely distance; and selecting a time cell containing θ or φ as a time cell that should contain the intersection based on the selected S1 or S2. the method of claim 1 further comprising. 6. The data storage medium is a magnetic disk (H
D), a group including a digital video disk (DVD), a magneto-optical disk (MO), a compact disk (CD), and a laser disk (LD). The method of claim 1. 7. A device for binarizing a read signal from a medium in which data is stored, comprising: a circuit for generating a slice signal; and a read signal using the slice signal. A level comparator for slicing a signal and detecting an intersection of a read signal and a slice signal, a circuit for generating and controlling a time cell, and selecting a time cell including the detected intersection, A phase comparator for detecting the phase difference between the center of the time cell and the intersection, and evaluating the likelihood of the time cell including the intersection using the detected phase difference, and selecting a time cell that should include the intersection. Operation evaluation circuit , wherein the operation evaluation circuit includes a selected time cell and two time cells before and after the selected time cell.
The phase difference between the center of each
Identify the time cell selected using the three phase differences
Of the three time cells.
The most likely time cell that should contain the difference
Selecting a time cell to be determined . 8. The arithmetic evaluation circuit according to claim 1, wherein the following two straight lines L0 and L1
L0 = f (p (0), p (1), θ) L1 = f (p (0), p (1), φ) where θ: the center of the time cell where the intersection is detected and the intersection Φ: phase difference between the center and the intersection of each of the two time cells before and after the time cell at which the intersection was detected and the phase difference of the smaller absolute value of the phase differences θ-1 and θ + 1 , P (0): value (phase difference) two times before, p (1): previous value (phase difference), distance D0 between straight line L0 and p (1) and distance D1 between straight line L1 and p (1) Selecting the smaller of D0 and D1 as a probable sum, and selecting a time cell containing θ or φ based on the selected D0 or D1 as a probable time cell in which the intersection should be included. The device according to claim 7 . 9. The operation evaluation circuit according to claim 2, wherein the following two straight lines L0 and L1
L0 = f (p (0), p (1), θ) L1 = f (p (0), p (1), φ) where θ: the center of the time cell where the intersection is detected and the intersection Φ: phase difference between the center and the intersection of each of the two time cells before and after the time cell at which the intersection was detected and the phase difference of the smaller absolute value of the phase differences θ-1 and θ + 1 , P (0): the value (phase difference) two times before, p (1): the previous value (phase difference), the sum A0 of the distance between the straight line L0 and p (0), p (1) and θ, and Obtain the sum A1 of the distances between the straight line L1 and p (0), p (1), and φ, select the smaller one of A0 and A1 as a likely sum, and based on the selected A0 or A1, θ or of claim 7, comprising, selecting a time cell as probable time cell should include the intersection including φ Location. 10. The arithmetic evaluation circuit calculates an average value α of phase differences selected up to the previous time, and calculates an average value α and a phase difference θ between the center of the currently selected time cell and the intersection. A distance d1 and an average value α;
The distance d2 between the phase difference θ-1 between the center of each of the two time cells before and after the time cell selected this time and the intersection and the smaller phase difference φ of θ + 1, the smaller of d1 and d2 to select as the probable distance, claim 7 comprising, selecting a time cell containing θ or φ based on the selected d1 or d2 as time cell should include the intersection The described device. 11. The arithmetic evaluation circuit obtains a linear function F from the phase difference selected up to the previous time, extrapolates the linear function F, predicts the current observation value β, and selects the observation value β and the currently selected observation value β. The distance S1 between the center of the time cell and the phase difference θ between the intersection and the observed value β;
A distance S2 between a smaller phase difference φ of the phase differences θ-1 and θ + 1 between the center of each of the two time cells before and after the time cell selected this time and the intersection is obtained, S1 and selecting S2 is smaller of the probable distance, according to claim 7 further comprising the, to select a time cell as time cell should include the intersections comprising based θ or φ to S1 or S2 is selected Equipment. 12. A circuit for generating and controlling said time cell, comprising a digital phase lock loop (PL).
The apparatus of claim 7, which is an L) circuit. 13. The data storage medium includes a magnetic disk (HD), a digital video disk (DVD), a magneto-optical disk (MO), and a compact disk (C).
8. The device according to claim 7 , wherein the device is selected from a group comprising D), a laser disk (LD).